Integrated environmentally insensitive modulator for interferometric gyroscopes

ABSTRACT

In an example, an integrated optical circuit (IOC) includes a first substrate formed of a first material and a first waveguide formed of a second material and positioned on the first substrate. The first waveguide includes a plurality of branches and is configured to polarize light beams that propagate through the first waveguide. The IOC further includes a second substrate formed of a third material, the second substrate coupled to or positioned on the first substrate. The IOC further includes a plurality of straight waveguides formed in the second substrate, each of the plurality of straight waveguides optically coupled to a respective branch of the plurality of branches of the first waveguide. The IOC further includes a plurality of electrodes positioned proximate to the plurality of straight waveguides, the plurality of electrodes configured to modulate the phase of light beams that propagate through the plurality of straight waveguides.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/869,425, filed May 7, 2020, and titled “INTEGRATED ENVIRONMENTALLYINSENSITIVE MODULATOR FOR INTERFEROMETRIC GYROSCOPES,” which is herebyincorporated herein by reference.

BACKGROUND

Typically, interferometric fiber optic gyroscopes include an integratedoptical circuit that performs three functions. In particular, theintegrated optical circuit operates as a 50/50 optical coupler, a phasemodulator, and a polarizer. The integrated optical circuit receives asingle beam of light, polarizes the light (for example, using annealedproton exchanged portions of a waveguide), splits the polarized light(for example, using a Y-junction), and passes the light through phasemodulators. To prevent environmental instability, titanium indiffusedwaveguides can be used for the phase modulators and stitched togetherwith the annealed proton exchanged portions of the waveguide.

Integrated optical circuits for interferometric gyroscope are generallymonolithic lithium niobate devices because lithium niobate isparticularly well suited for performing phase modulation. In order toreduce size, weight, and cost of interferometric gyroscopes, it isdesirable to increase the integration of functions into a single device(for example, the integrated optical circuit). However, lithium niobatedoes not lend itself to large scale integration of other functions dueto the physical properties of the material.

SUMMARY

In an example, an integrated optical circuit includes a first substrateformed of a first material and a first waveguide formed of a secondmaterial and positioned on the first substrate. The first waveguideincludes a plurality of branches and is configured to polarize lightbeams that propagate through the first waveguide. The integrated opticalcircuit further includes a second substrate formed of a third material,the second substrate coupled to or positioned on the first substrate.The integrated optical circuit further includes a plurality of straightwaveguides formed in the second substrate, each of the plurality ofstraight waveguides optically coupled to a respective branch of theplurality of branches of the first waveguide. The integrated opticalcircuit further includes a plurality of electrodes positioned proximateto the plurality of straight waveguides, the plurality of electrodesconfigured to modulate the phase of light beams that propagate throughthe plurality of straight waveguides.

DRAWINGS

Understanding that the drawings depict only some embodiments and are nottherefore to be considered limiting in scope, the exemplary embodimentswill be described with additional specificity and detail using theaccompanying drawings, in which:

FIG. 1 is a top view of an example integrated optical circuit;

FIGS. 2A-2B are cross-sectional, side views of example integratedoptical circuits;

FIG. 3 is a top view of an example integrated optical circuit;

FIGS. 4A-4C are cross-sectional, side views of example integratedoptical circuits;

FIG. 5 is a diagram of an example interferometric gyroscope;

FIG. 6 is a flow diagram of an example method of manufacturing anintegrated optical circuit; and

FIG. 7 is a flow diagram of an example method of manufacturing anintegrated optical circuit.

In accordance with common practice, the various described features arenot drawn to scale but are drawn to emphasize specific features relevantto the example embodiments.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings that form a part hereof, and in which is shown byway of illustration specific illustrative embodiments. However, it is tobe understood that other embodiments may be utilized and that logical,mechanical, and electrical changes may be made. Furthermore, the methodpresented in the drawing figures and the specification is not to beconstrued as limiting the order in which the individual steps may beperformed. The following detailed description is, therefore, not to betaken in a limiting sense.

Systems and methods for an integrated optical circuit forinterferometric gyroscopes are provided herein. The integrated opticalcircuit utilizes a first substrate with a first waveguide forpolarization and splitting functions and utilizes a second substrate andsecond waveguides for phase modulation. The first waveguide and thesecond waveguides are optically coupled and the second substrate iseither deposited on the first substrate or otherwise physically coupledto the first substrate. In some examples, the first waveguide can beformed from a material that is transparent at the operating wavelength(for example, silicon nitride, titanium dioxide, or silicon oxynitride)and the second waveguides can be formed from a material that has anon-zero second-order nonlinear coefficient (for example, lithiumniobate or lithium tantalate). By using different substrates rather thana single monolithic substrate, smaller size and/or better integration offunctionality can be achieved than with previous designs whilemaintaining a high level of performance.

FIG. 1 is a top view of an example integrated optical circuit 100. Inthe example shown in FIG. 1 , the integrated optical circuit 100includes a first substrate 102 and a second substrate 104 coupled to orpositioned on the first substrate 102. A first waveguide 106 is formedon the first substrate 102 and second waveguides 112 are formed in thesecond substrate 104 and positioned proximate to electrodes 114.

The first substrate 102 is formed of a first material. In some examples,the first material is silicon. In other examples, other similarmaterials can be used for the first substrate 102. In the example shownin FIG. 1 , a first waveguide 106 is positioned on the first substrate102. The first waveguide 106 is formed from a second material that isdifferent than the first material. In some examples, the first waveguide106 is formed of silicon nitride. In some examples, the first waveguide106 is formed of another material, such as, for example, titaniumdioxide, silicon oxynitride, or another material that is transparent atan operating wavelength of the integrated optical circuit (for example,1550 nm). The second material used for the first waveguide 106 has ahigher refractive index than the surrounding material, which includesthe first substrate 102 and any material used for cladding.

In the example shown in FIG. 1 , the first waveguide 106 includes aninput section 108 and multiple branches 110 that form a Y-junction. Thefirst waveguide 106 functions as a splitter for light that is input intothe first waveguide 106 at the input section 108. In some examples, thefirst waveguide 106 is configured to polarize light beams that propagatethrough the first waveguide 106. In some examples, the dimensions (forexample, width or height) of the first waveguide 106 can be selected toachieve the desired polarization of light propagating through the firstwaveguide 106. In some examples, the dimensions (for example, width andheight) of the first waveguide 106 are varied over the length of theinput section 108 and/or the branches 110 of the first waveguide 106.

In the example shown in FIG. 1 , the second substrate 104 is coupled toor positioned on the first substrate 102. The second substrate 104 isformed of a third material that is different from the first material andthe second material, and the third material has particular non-linearelectro-optic properties that are suitable for phase modulation for aninterferometric gyroscope. In some examples, the third material is alithium niobate. In other examples, the second substrate 104 is formedof lithium tantalate substrate or another material that has a non-zerosecond-order nonlinear coefficient.

In the example shown in FIG. 1 , two straight waveguides 112 are formedin the second substrate 104 and each of the straight waveguides 112 isoptically coupled to a respective branch 110 of the first waveguide 106.In some examples, there is an intermediate stage configured tofacilitate the optical signal transition between the branches 110 of thefirst waveguide 106 and the straight waveguides 112. In some examples,the straight waveguides 112 are coupled to the branches 110 of the firstwaveguide 106 via an adiabatic coupling, which can minimize opticalloss. In some examples, the straight waveguides 112 are titaniumindiffused waveguides formed in the second substrate 104. Since titaniumis not mobile inside the second substrate (for example, lithium niobateor lithium tantalate), titanium indiffused waveguides are moreenvironmentally stable than other types of waveguides (for example,proton exchanged waveguides). In other examples, a different type ofwaveguide can be formed or patterned in the second substrate 104 (forexample, by in-diffusion and etching).

In the example shown in FIG. 1 , electrodes 114 are positioned proximateto the straight waveguides 112 in the second substrate 104. The featuresof the second substrate 104 are configured to modulate the phase oflight propagating through the straight waveguides 112. In some examples,the electrodes 114 are configured to modulate the phase of light beamsthat propagate through the straight waveguides 112 of the secondsubstrate 104.

As discussed below with respect to FIGS. 6-7 , the integrated opticalcircuit 100 can be manufactured in different ways, which result is somedifferent physical characteristics for the integrated optical circuit100. However, the operation of the integrated optical circuit 100 issimilar regardless of the manufacturing used to make the integratedoptical circuit 100.

FIG. 2A is a cross-sectional, side view of an example of the integratedoptical circuit 100 shown in FIG. 1 where the second substrate 104 iscoupled to the first substrate 102. In such examples, the firstsubstrate 102 and the second substrate 104 are formed separately andphysically coupled together. In some examples, the first substrate 102and the second substrate 104 are bonded or coupled together using anadhesive. The example integrated optical circuit 200 shown in FIG. 2Acan be manufactured using the method described with respect to FIG. 6 .

FIG. 2B is a cross-sectional, side view of an example of the integratedoptical circuit 100 shown in FIG. 1 where the second substrate 104 ispositioned on the first substrate 102. In such examples, the firstsubstrate 102 is a common substrate for the first waveguide 106 and thesecond substrate 104 with the straight waveguides 112. In some examples,the second substrate 104 is deposited or grown on the first substrate102 and the straight waveguides 112 are formed in the second substrate104 (for example, by in-diffusion and etching). The example integratedoptical circuit 250 shown in FIG. 2B can be manufactured using themethod described with respect to FIG. 7 , which can be easier tomanufacture compared to the example shown in FIG. 2A.

FIG. 3 is a top view of an example integrated optical circuit 300. Inthe example shown in FIG. 3 , the integrated optical circuit 300includes a first substrate 302 and a second substrate 304 coupled to orpositioned on the first substrate 302. A first waveguide 306 is formedon the first substrate 302 and straight waveguides 312 are formed in thesecond substrate 304 and positioned proximate to electrodes 314. In theexample shown in FIG. 3 , the integrated optical circuit 300 furtherincludes second straight waveguides 316, which are formed on the firstsubstrate 302 or a third substrate 305.

The first substrate 302 is formed of a first material. In some examples,the first material is silicon. In other examples, other similarmaterials can be used for the first substrate 302. In the example shownin FIG. 3 , a first waveguide 306 is positioned on the first substrate302. The first waveguide 306 is formed from a second material that isdifferent than the first material. In some examples, the first waveguide306 is formed of silicon nitride. In some examples, the first waveguide306 is formed of another material, such as, for example, titaniumdioxide, silicon oxynitride, or another material that is transparent atan operating wavelength of the integrated optical circuit (for example,1550 nm). The second material used for the first waveguide 306 has ahigher refractive index than the surrounding material, which includesthe first substrate 302 and any material used for cladding.

In the example shown in FIG. 3 , the first waveguide 306 includes aninput section 308 and multiple branches 310 that form a Y-junction. Thefirst waveguide 306 functions as a splitter for light that is input intothe first waveguide 306 at the input section 308. In some examples, thefirst waveguide 306 is configured to polarize light beams that propagatethrough the first waveguide 306. In some examples, the dimensions (forexample, width or height) of the first waveguide 306 can be selected toachieve the desired polarization of light propagating through the firstwaveguide 306. In some examples, the dimensions (for example, width andheight) of the first waveguide 306 are varied over the length of theinput section 308 and/or the branches 310 of the first waveguide 306.

In the example shown in FIG. 3 , the second substrate 304 is coupled toor positioned on the first substrate 302. The second substrate 304 isformed of a third material that is different from the first material andthe second material, and the third material has particular non-linearelectro-optic properties that are suitable for phase modulation for aninterferometric gyroscope. In some examples, the third material is alithium niobate. In other examples, the second substrate 304 is formedfrom lithium tantalate substrate or another material that has a non-zerosecond-order nonlinear coefficient.

In the example shown in FIG. 3 , two straight waveguides 312 are formedin the second substrate 304 and each of the straight waveguides 312 isoptically coupled to a respective branch 310 of the first waveguide 306.In some examples, the straight waveguides 312 are coupled to thebranches 310 of the first waveguide 306 via an adiabatic coupling, whichcan minimize optical loss. In some examples, there is an intermediatestage configured to facilitate the optical signal transition between thebranches 310 of the first waveguide 306 and the straight waveguides 312.In some examples, the straight waveguides 312 are titanium indiffusedwaveguides formed in the second substrate 304. Since titanium is notmobile inside the second substrate (for example, lithium niobate orlithium tantalate), titanium indiffused waveguides are moreenvironmentally stable than other types of waveguides (for example,proton exchanged waveguides). In other examples, a different type ofwaveguide can be formed or patterned in the second substrate 304 (forexample, by in-diffusion and etching).

In the example shown in FIG. 3 , electrodes 314 are positioned proximateto the straight waveguides 312 in the second substrate 304. The featuresof the second substrate 304 are configured to modulate the phase oflight propagating through the straight waveguides 312. In some examples,the electrodes 314 are configured to modulate the phase of light beamsthat propagate through the straight waveguides 312 of the secondsubstrate 304.

In the example shown in FIG. 3 , the integrated optical circuit 300includes additional straight waveguides 316 that are positioned oneither the first substrate 302 or a third substrate 305 that is separatefrom the first substrate 302 and the second substrate 304. Each of theadditional straight waveguides 316 is optically coupled to a respectivestraight waveguide 312 formed in the second substrate 304. In someexamples, there is an intermediate stage configured to facilitate theoptical signal transition between the straight waveguides 312 of thesecond substrate 304 and the additional straight waveguides 316. Theadditional straight waveguides 316 are used to fine tune thepolarization of the light after phase modulation. In some examples, thedimensions (for example, width or height) of the additional straightwaveguides 316 can be selected to achieve the desired polarization oflight propagating through the additional straight waveguides 316. Insome examples, the dimensions (for example, width and height) of theadditional straight waveguides 316 are varied over the length of theadditional straight waveguides 316.

As discussed below with respect to FIGS. 6-7 , the integrated opticalcircuit 300 can be manufactured in different ways, which result is somedifferent physical characteristics for the integrated optical circuit300. However, the operation of the integrated optical circuit 300 issimilar regardless of the manufacturing used to make the integratedoptical circuit 300.

FIG. 4A is a cross-section view of an example of an integrated opticalcircuit 300 shown in FIG. 3 where the first substrate 302 is coupled tothe second substrate 304 and the second substrate 304 is coupled to athird substrate 305. In such examples, the first substrate 302, thesecond substrate 304, and the third substrate 305 are formed separatelyand physically coupled together. In some examples, the first substrate302, the second substrate 304, and the third substrate 305 are bonded orcoupled together using an adhesive. The example integrated opticalcircuit 400 shown in FIG. 4A can be manufactured using the methoddescribed with respect to FIG. 6 .

In the example shown in FIG. 4A, the additional straight waveguides 316are positioned on the third substrate 305 that is separate from thefirst substrate 302 and the second substrate 304. In such examples, thethird substrate 305 can be formed from the same material as the firstsubstrate 302 (first material) or a fourth material suitable as asubstrate that is different than the other materials discussed above. Insome such examples, the additional straight waveguides 316 are formedfrom the same material as the first waveguide 306 (second material) orfrom a different material that has a higher refractive index thansurrounding materials including the third substrate 305 and any claddingmaterial. In some examples, the additional straight waveguides 316 canbe formed from silicon nitride, titanium dioxide, silicon oxynitride, oranother material that is transparent at an operating wavelength of theintegrated optical circuit (for example, 1550 nm).

FIG. 4B is a cross-section view of an alternative example of theintegrated optical circuit 300 shown in FIG. 3 where the secondsubstrate 304 is positioned on the first substrate 302 and the firstsubstrate 302 is a common substrate for the first waveguide 306, thesecond substrate 304 with the straight waveguides 312, and theadditional straight waveguides 316. In some examples, the secondsubstrate 304 is deposited or grown on the first substrate 302 and thefirst set of straight waveguides 312 are formed in the second substrate304 (for example, by in-diffusion and etching). The example integratedoptical circuit 425 shown in FIG. 4B can be manufactured using themethod described with respect to FIG. 7 , which can be easier tomanufacture compared to the example shown in FIG. 4A.

In the example shown in FIG. 4B, the additional straight waveguides 316are positioned on the first substrate 302. In such examples, theadditional straight waveguides 316 can be formed from the same materialas the first waveguide 306 (the second material) or from a differentmaterial that has a higher refractive index than surrounding materialsincluding the first substrate 302 and any cladding material. In someexamples, the additional straight waveguides 316 can be formed fromsilicon nitride, titanium dioxide, silicon oxynitride, or anothermaterial that is transparent at an operating wavelength of theintegrated optical circuit (for example, 1550 nm).

FIG. 4C is a cross-section view of an alternative example of theintegrated optical circuit 300 shown in FIG. 3 where the secondsubstrate 304 is positioned on the first substrate 302, but the firstsubstrate 302 is not a common substrate for the additional straightwaveguides 316. In some examples, the second substrate 304 is depositedor grown on the first substrate 302 and the first set of straightwaveguides 312 are formed in the second substrate 304 (for example, byin-diffusion and etching). In such examples, the first substrate 302 andthe third substrate 305 are formed separately and physically coupledtogether. In some examples, the first substrate 302 and the thirdsubstrate 305 are bonded or coupled together using an adhesive. Theexample integrated optical circuit 450 shown in FIG. 4B can bemanufactured using a hybrid of the methods described with respect toFIGS. 6-7 .

In the example shown in FIG. 4C, the additional straight waveguides 316are positioned on the third substrate 305 that is separate from thefirst substrate 302 and the second substrate 304. In such examples, thethird substrate 305 can be formed from the same material as the firstsubstrate 302 (first material) or a fourth material suitable as asubstrate that is different than the other materials discussed above. Insome such examples, the additional straight waveguides 316 are formedfrom the same material as the first waveguide 306 (second material) orfrom a different material that has a higher refractive index thansurrounding materials including the third substrate 305 and any claddingmaterial. In some examples, the additional straight waveguides 316 canbe formed from silicon nitride, titanium dioxide, silicon oxynitride, oranother material that is transparent at an operating wavelength of theintegrated optical circuit (for example, 1550 nm).

Typically, the front-end of an interferometric fiber optic gyroscopeincludes a light source that is separate from the integrated opticalcircuit and an optical fiber is used to couple the light into thewaveguides of the integrated optical circuit. Further, additionalcomponents that are beneficial for monitoring and controlling operationof the integrated optical circuit and interferometric gyroscope are alsoseparate from the integrated optical circuit. By having these additionalcomponents separate from the integrated optical circuit, the previousdesigns can have significant disadvantages from a size, weight, and costperspective.

By using multiple substrates and different materials for the waveguidesas discussed above, the integrated optical circuits 100, 300 can includea greater amount of integration on the integrated optical circuits 100,300 (for example, more components on the integrated optical circuit) andreduce the size, weight, and cost of the integrated optical circuits100, 300 and/or an interferometric gyroscope that includes theintegrated optical circuits 100, 300. For example, by using a differentmaterial to form the first waveguide 106, 306 (for example, siliconnitride) than the material used for phase modulation (for example,lithium niobate or lithium tantalate), the first waveguide 106, 306 canhave significantly better mode confinement than previous designs and thesize of the first waveguide 106, 306 can be reduced without degradedperformance. In some examples, the length of the input section 108, 308of the first waveguide 106, 306 could be shortened and the angle of theY-junction can be made steeper.

In some examples, the integrated optical circuits 100, 300 include anintegrated light source (not shown) mounted to the first substrate 102,302, and the integrated light source is optically coupled to the inputsection 108, 308 of the first waveguide 106, 306. In some examples, theintegrated light source is a semiconductor or solid-state laser lightsource configured to provide the light signal for the integrated opticalcircuit 100, 300. Significant reductions in size, weight, and cost canbe achieved over previous designs by using an integrated optical circuitwith an integrated light source.

In some examples, the integrated optical circuits 100, 300 include oneor more integrated tap couplers (not shown) configured to couple lightfrom the first waveguide 106, 306. In some examples, the one or moreintegrated tap couplers are configured to couple a portion of light fromthe first waveguide 106, 306 and provide the coupled light to anothercomponent on the integrated optical circuit 100, 300. In some examples,the one or more integrated tap couplers are configured to provide thecoupled light to one or more integrated photodetectors on the integratedoptical circuit 100, 300, which can be mounted or disposed on the firstsubstrate 102, 302. In some examples, the one or more integratedphotodetectors are photodiodes. In some examples, one or more integratedtap couplers are configured to provide light to a rate detector.

FIG. 5 is a block diagram of an example interferometric gyroscope 500.In the example shown in FIG. 5 , the interferometric gyroscope 500includes a light source 502, a coupler 504, an integrated opticalcircuit 506, and a sensing coil 508. While the integrated opticalcircuit 506 shown in FIG. 5 corresponds to the integrated opticalcircuit 100 shown in FIG. 1 , it should be understood that theintegrated optical circuit 506 can comprise any of the integratedoptical circuits 100, 300 discussed above with respect to FIGS. 1-4C.

The light source 502 is configured to generate a light signal that is tobe coupled into the sensing coil 508. In some examples, the light source502 is a broadband light source configured to generate a light signalthat is comprised of many waves with different wavelengths andpolarization states. In the example shown in FIG. 5 , the light source502 is separate from the integrated optical circuit 506. In otherexamples, the light source 502 is integrated on the integrated opticalcircuit 506 as discussed above.

In the example shown in FIG. 5 , the coupler 504 is included between thelight source 502 and the integrated optical circuit 506. In exampleswhere the light source 502 is separate from the integrated opticalcircuit 506, the light source 502 is optically coupled to the integratedoptical circuit 506 using one or more optical fibers and the coupler504. For example, the optical fiber optically coupled to the lightsource 502 can extend through the coupler 504 and be optically coupledto a waveguide of the integrated optical circuit 506 (for example, thefirst waveguide 106, 306 as discussed above with respect to FIGS. 1-4C).In some examples, the coupler 504 includes both the optical fiber tooptically couple the light source to the integrated optical circuit andan output optical fiber configured to carry a returned signal from thephase modulators to a rate detector that reads the returning signal fromthe sensing coil 508.

In examples where the light source 502 is integrated on the integratedoptical circuit 506, the light source 502 itself is optically coupled toa waveguide of the integrated optical circuit 506 (for example, thefirst waveguide 106, 306 as discussed above with respect to FIGS. 1-4C).In such examples, the coupler 504 is also integrated on the integratedoptical circuit 506. In some examples, the integrated coupler 504 can beimplemented using a tap coupler as discussed above.

In the example shown in FIG. 5 , the sensing coil 508 is opticallycoupled to the integrated optical circuit 506. In some examples, thesensing coil 508 is optically coupled to the straight waveguides (forexample, waveguides 112, 312, or 316 as discussed above with respect toFIGS. 1-4C) of the integrated optical circuit 506 using pigtail fibers.The sensing coil 508 is configured to receive light signals from theintegrated optical circuit 506 and to output light signals to theintegrated optical circuit 506.

FIG. 6 is a flow diagram for a method 600 of manufacturing an integratedoptical circuit. The functions, structures, and other description ofliked-named elements for such examples described herein may apply tolike-named elements described with reference to the method 600 and viceversa.

The method 600 includes depositing a waveguide material on a firstsubstrate and patterning a first waveguide (block 602). The waveguidematerial can be deposited and patterned using known thin filmtechniques. In some examples, the first waveguide has an input sectionand multiple branches similar to the first waveguides discussed abovewith respect to FIGS. 1-4C. In some examples, the first substrate isformed from a first material (for example, silicon) and the waveguidematerial is different than the first material. In some examples, thewaveguide material is silicon nitride. In some examples, the waveguidematerial is formed of another material, such as, for example, titaniumdioxide, silicon oxynitride, or other material that is transparent at anoperating wavelength of the integrated optical circuit (for example,1550 nm). The waveguide material has a higher refractive index than thesurrounding material, which includes the first substrate and anymaterial used for cladding.

The method 600 further includes forming straight waveguides in a secondsubstrate (block 604). In some examples, the second substrate is formedof a third material that is different from the first material and thesecond material, and the third material has particular non-linearelectro-optic properties that are suitable for phase modulation for aninterferometric gyroscope. In some examples, the third material is alithium niobate. In other examples, the third material is lithiumtantalate or another material that has a non-zero second-order nonlinearcoefficient. In some examples, the straight waveguides are formed bydiffusing titanium waveguide material into the second substrate. In someexamples, the straight waveguides are formed by in-diffusion and etching(for example, deep ion etching).

The method 600 further includes physically coupling the first substrateand the second substrate and optically coupling the first waveguide andthe straight waveguides (block 606). In some examples, the firstsubstrate and the second substrate are bonded or coupled together usingan adhesive. In some examples, the branches of the first waveguide areoptically coupled to the straight waveguides formed in the secondsubstrate via an adiabatic coupling. In some examples, there is anintermediate stage configured to facilitate the optical signaltransition between the branches of the first waveguide and the straightwaveguides.

The method 600 optionally includes depositing a waveguide material on athird substrate and patterning additional straight waveguides on thethird substrate (block 608). The waveguide material can be deposited andpatterned using known thin film techniques. In some examples, the thirdsubstrate is formed from the same material as the first substrate (firstmaterial) or a fourth material suitable as a substrate that is differentthan the other materials discussed above. In some such examples, theadditional straight waveguides are formed from the same material as thefirst waveguide (second material) or from a different material that hasa higher refractive index than surrounding materials including the thirdsubstrate and any cladding material. In some examples, the additionalstraight waveguides can be formed from silicon nitride, titaniumdioxide, silicon oxynitride, or another material that is transparent atan operating wavelength of the integrated optical circuit (for example,1550 nm).

The method 600 optionally includes physically coupling the secondsubstrate and the third substrate and optically coupling the straightwaveguides of the second substrate and the additional straightwaveguides of the third substrate (block 610). In some examples, thesecond substrate and the third substrate are bonded or coupled togethervia an adhesive. In some examples, the straight waveguides of the secondsubstrate and the additional straight waveguides of the third substrateare optically coupled via an adiabatic coupling. In some examples, thereis an intermediate stage configured to facilitate the optical signaltransition between the straight waveguides formed in the secondsubstrate and the additional straight waveguides on the third substrate.

FIG. 7 is a flow diagram of a method 700 of manufacturing an integratedoptical circuit. The functions, structures, and other description ofliked-named elements for such examples described herein may apply tolike-named elements described with reference to the method 700 and viceversa.

The method 700 includes depositing waveguide material on a firstsubstrate and patterning a first waveguide (block 702). The waveguidematerial can be deposited and patterned using known thin filmtechniques. In some examples, the first waveguide has an input sectionand multiple branches similar to the first waveguides discussed abovewith respect to FIGS. 1-4C. In some examples, the first substrate isformed from a first material (for example, silicon) and the waveguidematerial is different than the first material. In some examples, thewaveguide material is silicon nitride. In some examples, the waveguidematerial is formed of another material, such as, for example, titaniumdioxide, silicon oxynitride, or another material that is transparent atan operating wavelength of the integrated optical circuit (for example,1550 nm). The waveguide material has a higher refractive index than thesurrounding material, which includes the first substrate and anymaterial used for cladding.

The method 700 further includes depositing or growing a second substrateon a portion of the first substrate (block 704). In some examples, thesecond substrate is grown on the first substrate using molecular beamepitaxy (MBE) or other thin film techniques.

The method 700 further includes forming straight waveguides in thesecond substrate (block 706). In some examples, the second substrate isformed of a third material that is different from the first material andthe second material, and the third material has particular non-linearelectro-optic properties that are suitable for phase modulation for aninterferometric gyroscope. In some examples, the third material is alithium niobate. In other examples, the third material is lithiumtantalate or another material that has a non-zero second-order nonlinearcoefficient. In some examples, the straight waveguides are formed bydiffusing titanium waveguide material into the second substrate. In someexamples, the straight waveguides are formed by in-diffusion and etching(for example, deep ion etching).

The method 700 optionally includes depositing waveguide material on thefirst substrate and patterning additional straight waveguides on thefirst substrate (block 708). The waveguide material can be deposited andpatterned using known thin film techniques. In some examples, theadditional straight waveguides are similar to the additional straightwaveguides discussed above with respect to FIGS. 3-4C. In some examples,the additional straight waveguides are formed from the same material asthe first waveguide (second material) or from a different material thathas a higher refractive index than the first substrate and any claddingmaterial. In some examples, the additional straight waveguides can beformed from silicon nitride, titanium dioxide, silicon oxynitride, orother material that is transparent at an operating wavelength of theintegrated optical circuit (for example, 1550 nm).

In various aspects, system elements, method steps, or examples describedthroughout this disclosure may be implemented on one or more computersystems, field programmable gate array (FPGA), application specificintegrated circuit (ASIC) or similar devices comprising hardwareexecuting code to realize those elements, processes, or examples, saidcode stored on a non-transient data storage device. These devicesinclude or function with software programs, firmware, or other computerreadable instructions for carrying out various methods, process tasks,calculations, and control functions, used for synchronization and faultmanagement in a distributed antenna system.

These instructions are typically stored on any appropriate computerreadable medium used for storage of computer readable instructions ordata structures. The computer readable medium can be implemented as anyavailable media that can be accessed by a general purpose or specialpurpose computer or processor, or any programmable logic device.Suitable processor-readable media may include storage or memory mediasuch as magnetic or optical media. For example, storage or memory mediamay include conventional hard disks, Compact Disk-Read Only Memory(CD-ROM), volatile or non-volatile media such as Random Access Memory(RAM) (including, but not limited to, Synchronous Dynamic Random AccessMemory (SDRAM), Double Data Rate (DDR) RAM, RAMBUS Dynamic RAM (RDRAM),Static RAM (SRAM), etc.), Read Only Memory (ROM), Electrically ErasableProgrammable ROM (EEPROM), and flash memory, etc. Suitableprocessor-readable media may also include transmission media such aselectrical, electromagnetic, or digital signals, conveyed via acommunication medium such as a network and/or a wireless link.

The methods and techniques described here may be implemented in digitalelectronic circuitry, or with a programmable processor (for example, aspecial-purpose processor or a general-purpose processor such as acomputer) firmware, software, or in combinations of them. Apparatusembodying these techniques may include appropriate input and outputdevices, a programmable processor, and a storage medium tangiblyembodying program instructions for execution by the programmableprocessor. A process embodying these techniques may be performed by aprogrammable processor executing a program of instructions to performdesired functions by operating on input data and generating appropriateoutput. The techniques may advantageously be implemented in one or moreprograms that are executable on a programmable system including at leastone programmable processor coupled to receive data and instructionsfrom, and to transmit data and instructions to, a data storage system,at least one input device, and at least one output device. Generally, aprocessor will receive instructions and data from a read-only memoryand/or a random-access memory. Storage devices suitable for tangiblyembodying computer program instructions and data include all forms ofnon-volatile memory, including by way of example semiconductor memorydevices, such as EPROM, EEPROM, and flash memory devices; magnetic diskssuch as internal hard disks and removable disks; magneto-optical disks;and DVD disks. Any of the foregoing may be supplemented by, orincorporated in, specially-designed application-specific integratedcircuits (ASICs).

EXAMPLE EMBODIMENTS

Example 1 includes an integrated optical circuit, comprising: a firstsubstrate formed of a first material; a first waveguide formed of asecond material and positioned on the first substrate, wherein the firstwaveguide includes a plurality of branches and is configured to polarizelight beams that propagate through the first waveguide; a secondsubstrate formed of a third material, wherein the second substrate iscoupled to or positioned on the first substrate; a plurality of firststraight waveguides formed in the second substrate, wherein each of theplurality of first straight waveguides is optically coupled to arespective branch of the plurality of branches of the first waveguide;and a plurality of electrodes positioned proximate to the plurality offirst straight waveguides, wherein the plurality of electrodes isconfigured to modulate the phase of light beams that propagate throughthe plurality of first straight waveguides.

Example 2 includes the integrated optical circuit of Example 1, whereinthe second material is transparent at an operating wavelength of theintegrated optical circuit.

Example 3 includes the integrated optical circuit of Example 2, whereinthe second material is silicon nitride, titanium dioxide, or siliconoxynitride.

Example 4 includes the integrated optical circuit of any of Examples1-3, wherein the third material has a non-zero second-order nonlinearcoefficient.

Example 5 includes the integrated optical circuit of any of Examples1-4, wherein the third material is lithium niobate or lithium tantalate.

Example 6 includes the integrated optical circuit of any of Examples1-5, further comprising: a plurality of second straight waveguidespositioned on the first substrate, wherein each second straightwaveguide of the plurality of second straight waveguides is opticallycoupled to a respective first straight waveguide of the plurality offirst straight waveguides, wherein the plurality of first straightwaveguides is positioned between the first waveguide and the pluralityof second straight waveguides; wherein each respective second straightwaveguide of the plurality of second straight waveguides is configuredto polarize light beams that propagate through the respective secondstraight waveguide.

Example 7 includes the integrated optical circuit of any of Examples1-5, further comprising: a plurality of second straight waveguidespositioned on a third substrate, wherein each second straight waveguideof the plurality of second straight waveguides is optically coupled to arespective first straight waveguide of the plurality of first straightwaveguides, wherein the plurality of first straight waveguides ispositioned between the first waveguide and the plurality of secondstraight waveguides; wherein each respective second straight waveguideof the plurality of second straight waveguides is configured to polarizelight beams that propagate through the respective second straightwaveguide.

Example 8 includes the integrated optical circuit of any of Examples1-7, further comprising: a light source mounted on the first substrate,wherein the light source is optically coupled to the first waveguide andconfigured to generate a light signal.

Example 9 includes the integrated optical circuit of any of Examples1-8, wherein the second substrate is deposited or grown on the firstsubstrate, wherein the plurality of first straight waveguides is formedby in-diffusion and etching.

Example 10 includes the integrated optical circuit of any of Examples1-9, wherein the second substrate is bonded or coupled to the firstsubstrate via an adhesive.

Example 11 includes an interferometric gyroscope, comprising: anintegrated optical circuit, comprising: a first substrate formed of afirst material; a first waveguide formed of a second material andpositioned on the first substrate, wherein the first waveguide includesa plurality of branches and is configured to polarize light beams thatpropagate through the first waveguide; a second substrate formed of athird material, wherein the second substrate is coupled to or positionedon the first substrate; a plurality of first straight waveguides formedin the second substrate, wherein each of the plurality of first straightwaveguides is optically coupled to a respective branch of the pluralityof branches of the first waveguide; and a plurality of electrodespositioned proximate to the plurality of first straight waveguides,wherein the plurality of electrodes is configured to modulate the phaseof light beams that propagate through the plurality of first straightwaveguides; a light source configured to generate a light signal,wherein the light source is optically communicatively coupled to thefirst waveguide of the integrated optical circuit; and a sensing coilconfigured to receive signals from the integrated optical circuit andoutput signals to the integrated optical circuit.

Example 12 includes the interferometric gyroscope of Example 11, whereinthe second material is silicon nitride, titanium dioxide, or siliconoxynitride.

Example 13 includes the interferometric gyroscope of any of Examples11-12, wherein the third material is lithium niobate or lithiumtantalate.

Example 14 includes the interferometric gyroscope of any of Examples11-13, wherein the integrated optical circuit further comprises: aplurality of second straight waveguides positioned on the firstsubstrate, wherein each second straight waveguide of the plurality ofsecond straight waveguides is optically coupled to a respective firststraight waveguide of the plurality of first straight waveguides,wherein the plurality of first straight waveguides is positioned betweenthe first waveguide and the plurality of second straight waveguides;wherein each respective second straight waveguide of the plurality ofsecond straight waveguides is configured to polarize light beams thatpropagate through the respective second straight waveguide.

Example 15 includes the interferometric gyroscope of any of Examples11-13, further comprising: a plurality of second straight waveguidespositioned on a third substrate, wherein each second straight waveguideof the plurality of second straight waveguides is optically coupled to arespective first straight waveguide of the plurality of first straightwaveguides, wherein the plurality of first straight waveguides ispositioned between the first waveguide and the plurality of secondstraight waveguides; wherein each respective second straight waveguideof the plurality of second straight waveguides is configured to polarizelight beams that propagate through the respective second straightwaveguide.

Example 16 includes the interferometric gyroscope of any of Examples11-15, wherein the light source is mounted on the first substrate.

Example 17 includes the interferometric gyroscope of any of Examples11-16, wherein the second substrate is deposited or grown on the firstsubstrate, wherein the plurality of first straight waveguides is formedby in-diffusion and etching.

Example 18 includes the interferometric gyroscope of any of Examples11-17, wherein the second substrate is bonded or coupled to the firstsubstrate via an adhesive.

Example 19 includes an integrated optical circuit, comprising: a firstsubstrate formed of a first material; a first waveguide formed of asecond material and positioned on the first substrate, wherein the firstwaveguide includes a plurality of branches and is configured to polarizelight beams that propagate through the first waveguide; a secondsubstrate formed of a third material, wherein the second substrate iscoupled to or positioned on the first substrate; a plurality of firststraight waveguides formed in the second substrate, wherein each of theplurality of first straight waveguides is optically coupled to arespective branch of the plurality of branches of the first waveguide; aplurality of electrodes positioned proximate to the plurality of firststraight waveguides, wherein the plurality of electrodes is configuredto modulate the phase of light beams that propagate through theplurality of first straight waveguides; and a plurality of secondstraight waveguides formed of the second material and positioned on thefirst substrate or a third substrate, wherein each second straightwaveguide of the plurality of second straight waveguides is opticallycoupled to a respective first straight waveguide of the plurality offirst straight waveguides, wherein the plurality of first straightwaveguides is positioned between the first waveguide and the pluralityof second straight waveguides, wherein each respective second straightwaveguide of the plurality of second straight waveguides is configuredto polarize light beams that propagate through the respective secondstraight waveguide.

Example 20 includes the integrated optical circuit of Example 19,wherein the second material is silicon nitride, titanium dioxide, orsilicon oxynitride; and wherein the third material is lithium niobate orlithium tantalate.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement, which is calculated to achieve the same purpose,may be substituted for the specific embodiments shown. Therefore, it ismanifestly intended that this invention be limited only by the claimsand the equivalents thereof.

What is claimed is:
 1. An integrated optical circuit, comprising: afirst substrate formed of a first material; a first waveguide formed ofa second material and positioned on the first substrate, wherein thefirst waveguide is configured to polarize light beams that propagatethrough the first waveguide, wherein the first waveguide is configuredto split a light beam input into the first waveguide into multiple lightbeams; a second substrate formed of a third material, wherein the secondsubstrate is coupled to or positioned on the first substrate; and aplurality of phase modulators positioned on or in the second substrate,wherein each respective phase modulator of the plurality of phasemodulators is optically coupled to a respective branch of the firstwaveguide, wherein each respective phase modulator of the plurality ofphase modulators is configured to modulate a phase of light beams thatpropagate through the respective phase modulator.
 2. The integratedoptical circuit of claim 1, wherein the first waveguide includes aninput section and multiple branches that form a Y-junction.
 3. Theintegrated optical circuit of claim 1, wherein the second material has ahigher refractive index than the first material, wherein the thirdmaterial has a non-zero second-order nonlinear coefficient.
 4. Theintegrated optical circuit of claim 1, wherein the second material issilicon nitride, titanium dioxide, or silicon oxynitride, wherein thethird material is lithium niobate or lithium tantalate.
 5. Theintegrated optical circuit of claim 1, further comprising: a pluralityof straight waveguides positioned on the first substrate, wherein eachrespective straight waveguide of the plurality of straight waveguides isoptically coupled to a respective phase modulator of the plurality ofphase modulators positioned between the first waveguide and therespective straight waveguide of the plurality of straight waveguides;wherein each respective straight waveguide of the plurality of straightwaveguides is configured to polarize light beams that propagate throughthe respective straight waveguide of the plurality of straightwaveguides.
 6. The integrated optical circuit of claim 1, furthercomprising: a plurality of straight waveguides positioned on a thirdsubstrate, wherein each respective straight waveguide of the pluralityof straight waveguides is optically coupled to a respective phasemodulator of the plurality of phase modulators positioned between thefirst waveguide and the respective straight waveguide of the pluralityof straight waveguides; wherein each respective straight waveguide ofthe plurality of straight waveguides is configured to polarize lightbeams that propagate through the respective straight waveguide of theplurality of straight waveguides.
 7. The integrated optical circuit ofclaim 1, further comprising: a light source mounted on the firstsubstrate, wherein the light source is optically coupled to the firstwaveguide and configured to generate a light signal.
 8. The integratedoptical circuit of claim 1, wherein the second substrate is positionedon the first substrate, wherein the plurality of phase modulatorsincludes a plurality of indiffused waveguides.
 9. The integrated opticalcircuit of claim 1, wherein the second substrate is bonded or coupled tothe first substrate via an adhesive.
 10. An interferometric gyroscope,comprising: an integrated optical circuit, comprising: a first substrateformed of a first material; a first waveguide formed of a secondmaterial and positioned on the first substrate, wherein the firstwaveguide is configured to polarize light beams that propagate throughthe first waveguide, wherein the first waveguide is configured to splita light beam input into the first waveguide into multiple light beams; asecond substrate formed of a third material, wherein the secondsubstrate is coupled to or positioned on the first substrate; and aplurality of phase modulators positioned on or in the second substrate,wherein each respective phase modulator of the plurality of phasemodulators is optically coupled to a respective branch of the firstwaveguide, wherein each respective phase modulator of the plurality ofphase modulators is configured to modulate a phase of light beams thatpropagate through the respective phase modulator; a light sourceconfigured to generate a light signal, wherein the light source isoptically communicatively coupled to the first waveguide of theintegrated optical circuit; and a sensing coil configured to receivesignals from the integrated optical circuit and output signals to theintegrated optical circuit.
 11. The interferometric gyroscope of claim10, wherein the first waveguide includes an input section and multiplebranches that form a Y-junction.
 12. The interferometric gyroscope ofclaim 10, wherein the second material has a higher refractive index thanthe first material, wherein the third material has a non-zerosecond-order nonlinear coefficient.
 13. The interferometric gyroscope ofclaim 10, wherein the second material is silicon nitride, titaniumdioxide, or silicon oxynitride; wherein the third material is lithiumniobate or lithium tantalate.
 14. The interferometric gyroscope of claim10, wherein the integrated optical circuit further comprises: aplurality of straight waveguides positioned on the first substrate,wherein each respective straight waveguide of the plurality of straightwaveguides is optically coupled to a respective phase modulator of theplurality of phase modulators positioned between the first waveguide andthe respective straight waveguide of the plurality of straightwaveguides; wherein each respective straight waveguide of the pluralityof straight waveguides is configured to polarize light beams thatpropagate through the respective straight waveguide of the plurality ofstraight waveguides.
 15. The interferometric gyroscope of claim 10,further comprising: a plurality of straight waveguides positioned on athird substrate, wherein each respective straight waveguide of theplurality of straight waveguides is optically coupled to a respectivephase modulator of the plurality of phase modulators positioned betweenthe first waveguide and the respective straight waveguide of theplurality of straight waveguides; wherein each respective straightwaveguide of the plurality of straight waveguides is configured topolarize light beams that propagate through the respective straightwaveguide of the plurality of straight waveguides.
 16. Theinterferometric gyroscope of claim 10, wherein the light source ismounted on the first substrate.
 17. The interferometric gyroscope ofclaim 10, wherein the second substrate is positioned on the firstsubstrate, wherein the plurality of phase modulators include a pluralityof indiffused waveguides.
 18. The interferometric gyroscope of claim 10,wherein the second substrate is bonded or coupled to the first substratevia an adhesive.
 19. An integrated optical circuit, comprising: a firstsubstrate formed of a first material; a first waveguide formed of asecond material and positioned on the first substrate, wherein the firstwaveguide is configured to split and polarize light beams that propagatethrough the first waveguide; a second substrate formed of a thirdmaterial, wherein the second substrate is coupled to or positioned onthe first substrate; a plurality of phase modulators positioned on or inthe second substrate, wherein each respective phase modulator of theplurality of phase modulators is optically coupled to a respectivebranch of the first waveguide, wherein each respective phase modulatorof the plurality of phase modulators is configured to modulate a phaseof light beams that propagate through the respective phase modulator;and a plurality of straight waveguides formed of the second material andpositioned on the first substrate or a third substrate, wherein eachrespective straight waveguide of the plurality of straight waveguides isoptically coupled to a respective phase modulator of the plurality ofphase modulators positioned between the first waveguide and therespective straight waveguide of the plurality of straight waveguides,wherein each respective straight waveguide of the plurality of straightwaveguides is configured to polarize light beams that propagate throughthe respective straight waveguide of the plurality of straightwaveguides.
 20. The integrated optical circuit of claim 19, wherein thefirst waveguide includes an input section and multiple branches thatform a Y-junction.